The goal of this project is to guide the development of health policy regarding the appropriate use of genetic screening tests. These policies should be based in part on the accuracy of available screening tests, and in part on individuals' preferences for the information they provide. This project will study individuals' preferences for receiving genetic information made increasingly available through advances stemming from the Human Genome Project. The results will illuminate the important factors in individual judgments about the value of genetic carrier information. The project will use as a model prenatal and preconception carrier screening for five common mutations causing cystic fibrosis (deltaF508, G542X, F551D, R553X, N1303K). This is not a pilot clinical program for CF carrier testing; instead, the project investigates the decisions couples in such a program make. The study will test the hypothesis that when given the opportunity to learn genetic carrier information in sequence-by screening one partner in a couple at a time-many couples will in fact chose not to test the second partner. In doing so, these couples make a decision to obtain less than all of the obtainable information. Couples in both the prenatal setting and the preconception setting will be studied because their preferences for information are likely to be different. In this regard the project will investigate both the appropriate timing of carrier screening, and the amount that should be performed. The decision to obtain less than the maximum available information makes sense if the information is not useful in making future decisions, but has a negative impact on the way individuals perceive themselves. The results of this study will have important implications for the formulation of health study. If the study hypotheses are correct, the best public screening policy may be to recommended that only one partner in a couple by screened for CF mutations, and that the other partner should be screened only if the first is positive. If, on the other hand, the study hypotheses are incorrect, the results will suggest that individuals prefer carrier screening of both partners simultaneously, regardless of the potential problems of receiving information that they cannot effectively use.